Electrocapillary cleaning aids in dishwashers

ABSTRACT

The invention relates to a method for cleaning objects ( 3 ), particularly kitchenware ( 3 ), whereby the objects to be cleaned ( 3 ) are brought in contact with a washing liquid ( 5 ).  
     According to the invention, at least one electric field is generated in at least some parts of the surface of the objects to be cleaned ( 3 ).

The present invention relates to a method for cleaning objects,particularly kitchenware, whereby the objects to be cleaned are broughtin contact with a washing liquid. Moreover, the present inventionrelates to an apparatus for cleaning objects, particularly a dishwashingmachine, that brings the objects to be cleaned in contact with a washingliquid.

During recent years, a number of technical improvements have beendeveloped for dishwashing machines and such improved machines have beenbrought on the market. For example, the energy consumption per averagedishwashing cycle has been reduced from 3.1 kWz in 1965 to 1.05 kWhtoday. Moreover, water consumption has been reduced from 60 to 12 L anddetergent consumption from 40 to 25 g.

The object of the present invention is to further develop the methodsand equipment of the said kind so as to provide further savings inmachinery, energy consumption and/or water and/or detergent while at thesame time shortening the cleaning time without impairing the cleaningresults.

This objective can be reached through the features indicated in theindependent claims.

The method according to the invention is based on the prior art of thesaid kind in that an electric field is created in at least some areas ofthe surfaces of the objects to be cleaned, said field being imparted bythe washing liquid. This, on the one hand, brings about faster initialdissolution of the soil present on the objects to be cleaned, forexample on glass and/or porcelain and, on the other, the soil isdislodged from a larger surface area. By this effect, the same cleaningefficiency compared to the prior art can be achieved in a more effectivemanner and with a reduced consumption of water and/or energy and/ordetergents. The electric field is preferably an electrostatic field thegeneration of which requires no flow of electric current or requiresonly a very minor flow. The invention uses the physical and chemicaleffects of electrocapillarity, particularly electrically inducedpreferential wetting and electrosorption, which together are herereferred to as electrocapillary cleaning assistance. The assumedmechanism of electrocapillarity is the mutual repulsion, at theinterface, of charge carriers carrying charges of the same sign. Byelectrically induced preferential wetting is meant the influencing ofthe surface tension of liquids by an electric field. By electrosorptionis meant the influencing of adsorption or desorption of adsorbatemolecules at the solid-water interfaces by an electric field actingperpendicularly to the interfaces. A combination of these two physicaland chemical effects is, for example, the influencing of electricallyinduced preferential wetting by surfactants. For example, the curvesshowing electrically induced preferential wetting as a function ofelectric potential can be strongly influenced by the addition ofsurfactants having cleaning activity.

According to the method of the invention, the electric field preferablyhas a component that is perpendicular to the surfaces of the objects tobe cleaned. If the washing liquid contains surfactants, this componentcan be substantially smaller than required by the theory ofelectrocapillarity for a liquid devoid of surfactants.

In particularly preferred embodiments of the method of the invention,the electric field is generated by electrification of the washingliquid. In this case, the physical background of electrocapillarycleaning assistance lies in the fact that at the interface between thewashing liquid, particularly an aqueous solution, and the objects to becleaned, the electric field reduces the surface tension of the washingliquid thus improving the wetting on the surfaces of the objects to becleaned (electrically induced preferential wetting). If the washingliquid contains surfactants, they can be guided by the electric fieldselectively to the surfaces of the objects to be cleaned(electrosorption).

Moreover, in preferred embodiments of the method of the invention thewashing liquid contains substances with cleaning ability, particularlysurfactants and/or enzymes. Because of the electric field, thesubstances with cleaning ability can be guided rapidly to the objects tobe cleaned, resulting in more effective soil removal. If soil is removedat one spot, the washing liquid with its reduced surface tension can byelectrocapillarity penetrate more readily between the objects to becleaned and the soil, so that the soil is displaced more effectively.

Furthermore, in advantageous embodiments of the method of the inventionthe electrification of the washing liquid occurs by means of a firstelectrode to which is applied an electric potential. The washing liquidis thus electrified regardless of the presence of dissolved additives.The presence of substances with cleaning ability and particularly ofsurface-active substances, however, was found to be very advantageousfor the cleaning.

The method of the invention uses an electric potential in the range from100 volts to 10,000 volts and particularly from 1000 volts to 5,000volts. The polarity of the potential can be either positive or negative.A possible charge on ionic surfactants should therefore be the same asthe charge on the electrified washing liquid. The current can be eitherdirect or alternating.

Furthermore, in preferred embodiments of the method of the invention,the electrification electrode is disposed in the region of a section ofthe line through which the washing liquid flows before it comes incontact with the objects to be cleaned. In particular, the electrode canbe a metallic electrode.

As regards the method of the invention, the electrification electrodecan also be disposed in the region of a nozzle arm. In this case, forexample, a high voltage can be applied directly to a conductive nozzlethat is electrically insulated in a suitable manner.

In this respect in particular, by the method of the invention acounterelectrode can be disposed close to the objects to be cleaned. Theelectric field then decreases between the electrified washing liquid andthe counterelectrode. Embodiments are also possible, however, whereinthe counterelectrode is omitted, in which case the metallic objectspresent in the vicinity, for example the boundary of the inner cleaningspace, can act as the counterelectrode.

Moreover, by the method of the invention the washing liquid, aftercoming in contact with the objects to be cleaned, can be collected in acollecting container. As is known, for example, for dishwashingmachines, the washing liquid can be recycled by pumping for at least alength of time so that it can repeatedly be brought in contact with theobjects to be cleaned.

Furthermore, by the method of the invention the washing liquid, afterhaving at least once come in contact with the objects to be cleaned, canbe de-electrified at least in part. If the washing liquid is recycled bypumping so as to be repeatedly brought in contact with the objects to becleaned, it can be advantageous for the de-electrification to occur onlyafter the last contact with the objects to be cleaned has occurred.

In connection with the foregoing, in particular, by the method of theinvention the washing liquid can be at least partly de-electrifiedbefore it is disposed of. By disposal is meant in this respect, forexample, the final removal of the washing liquid by pumping it out ofthe dishwashing machine.

In preferred embodiments of the method of the invention, thede-electrification occurs with the aid of a de-electrificationelectrode. This electrode is preferably connected to a mass to permit apreferably complete electric discharge of the washing liquid.

In the afore-explained context, in particular, in certain preferredembodiments of the method of the invention, the de-electrificationelectrode can be located in the region of the collecting container.

Any apparatus that is suitable for carrying out an embodiment the methodof the invention falls under the protective scope of the related claims.

The apparatus according to the invention is based on the prior art ofthis kind in that it is provided with means that generate an electricfield at least in some regions of the surfaces of the objects to becleaned. In this manner, on the one hand, the soil on the objects to becleaned, for example on glass and/or porcelain, begins to dissolve morequickly and, on the other, the removal of soil from a larger surfacearea is achieved, as described for the method of the invention. By thesetwo effects, the same cleaning efficacy as that shown by the knownequipment of the same kind is achieved more rapidly and with a lowerconsumption of water and/or energy and/or cleaning agent. In this case,too, the electric field is preferably an electrostatic field thegeneration of which requires no flow of electric current or requiresonly a very minor flow. The apparatus according to the invention thusmakes use of the physical and chemical effects of electrically inducedpreferential wetting and electrosorption which together, as previouslystated, are also referred to as electrocapillary cleaning assistance.The assumed mechanism of electrocapillarity is the mutual repulsion, atthe interface, of charge carriers carrying charges of the same sign. Byelectrically induced preferential wetting is meant the influencing ofthe surface tension of liquids by an electric field. By electrosorptionis meant the electric potential-dependent influencing of adsorption ordesorption of adsorbate molecules at solid-water interfaces. Acombination of these two physical and chemical effects is, for example,the influencing of electrically induced preferential wetting bysurfactants, as previously explained for the method of the invention.For example, in the case of the apparatus of the invention, too, thecurves of electrically induced preferential wetting as a function ofelectric potential can be strongly influenced by the addition ofsurfactants showing cleaning activity.

Moreover, in the apparatus of the invention, the electrification meanspreferably generate an electric field over the surfaces of the objectsto be cleaned in a manner such that said field has a vertical componentover the objects to be cleaned.

In particularly preferred embodiments of the apparatus of the invention,the electrifying means electrify the washing liquid. In this case, thephysical background of electrocapillary cleaning assistance consists inthat the electric field, at the interface between the washing liquidparticularly water, and the objects to be cleaned reduces the surfacetension of the washing liquid thus improving the wetting on the surfacesof the objects to be cleaned (electrically induced preferentialwetting), as previously indicated for the method of the invention. Ifthe washing liquid contains surfactants, then in the case of theapparatus of the invention, too, they can be guided by the electricfield to the surfaces of the objects to be cleaned (electrosorption).

Furthermore, in the preferred embodiments of the apparatus according tothe invention, the washing liquid contains substances with cleaningactivity, particularly surfactants and/or enzymes. The substances withcleaning ability can, because of the electric field, be guided rapidlyto the objects to be cleaned, resulting in a more rapid soil removal. Ifsoil is removed at one spot, the washing liquid with a reduced surfacetension can penetrate more readily between the objects to be cleaned andthe soil, so that the soil is more effectively displaced. This hasalready been explained in connection with the method of the invention.

In advantageous embodiments of the apparatus of the invention, the meansfor electrifying the washing liquid comprise an electrificationelectrode to which an electric potential can be applied. The washingliquid is thus electrified regardless of the presence of dissolvedadditives. The presence of substances with cleaning ability andparticularly of surface-active substances, however, was found to be veryadvantageous for the cleaning, as already indicated in connection withthe method of the invention.

Moreover, it is also preferred that the positive or negative electricpotential for the apparatus of the invention be in the range from 100 to10,000 volts and particularly from 1000 to 5,000 volts. In this case,too, the current can be direct or alternating current.

Furthermore, in a preferred embodiment of the apparatus of theinvention, the electrifying electrode is disposed in the region of asection of the line through which the washing liquid flows before saidwashing liquid comes in contact with the objects to be cleaned. In thiscase, too, the electrode can, in particular, be a metallic electrode.

With respect to the apparatus of the invention, too, the electrificationelectrode can also be disposed in the region of a nozzle arm. In thiscase, for example, as has already been explained in connection with themethod of the invention, a high voltage can be applied directly to aconductive nozzle that is electrically insulated in a suitable manner.

In this respect in particular, in the apparatus of the invention acounterelectrode can be disposed close to the objects to be cleaned.Embodiments are also possible, however, wherein the counterelectrode isomitted, in which case the metallic objects present in the vicinity, forexample the boundary of the inner cleaning space, can act as thecounterelectrode, as has already been explained for the method of theinvention.

Furthermore, in the apparatus of the invention the washing liquid, aftercoming in contact with the objects to be cleaned, can be collected in acollecting container. As is known, for example, for dishwashingmachines, the washing liquid can, as indicated, be recycled by pumpingfor a certain period of time so that it can repeatedly be brought incontact with the objects to be cleaned.

Moreover, the apparatus of the invention can be provided with ade-electrification electrode for the purpose of at least partiallyde-electrifying the washing liquid after said liquid has at least oncecome in contact with the objects to be cleaned. In the event that thewashing liquid is recycled by pumping so as to be brought repeatedlyinto contact with the objects to be cleaned, it can be advantageous alsoin the case of the apparatus of the invention to undertake thede-electrification only after the last contact with the objects to becleaned has occurred.

Furthermore, in the afore-explained regard in particular, in theapparatus of the invention the de-electrification means will at leastpartially de-electrify the washing liquid before said washing liquid isdisposed of. By disposal is meant in this regard, too, the final removalof the washing liquid by pumping it out of the dishwashing machine.

In the preferred embodiments of the apparatus of the invention, too, thede-electrification means comprise a de-electrifying electrode. Saidelectrode is preferably connected to a mass to permit a preferablycomplete electric discharge of the washing liquid, as in the case of themethod of the invention.

In regard to the afore-explained context, in certain embodiments of theapparatus of the invention the de-electrifying electrode can be locatedin the region of the collecting container.

Furthermore, in the preferred embodiments of the apparatus of theinvention there is provided a protective circuit breaker that turns offthe power in the event of a predetermined current flow. In this case,the predetermined current flow is selected so that the power is shut offbefore reaching a level dangerous for humans.

In the following, the invention will be explained by reference to theattached drawings in which:

FIG. 1 is a schematic representation of the operating principle of theelectrocapillary cleaning effect;

FIG. 2 is a schematic representation of a first embodiment of theapparatus of the invention that is also suitable for carrying out themethod of the invention;

FIG. 3 shows two curves illustrating, for an electrified and anonelectrified washing liquid, the dislodgement of a test soil fromobjects to be cleaned; and

FIG. 4 is a schematic representation of a second embodiment of theapparatus of the invention in the form of a dishwashing machine.

FIG. 1 shows a schematic representation of the operating principle ofthe electrocapillary cleaning effect, here with positive charge carriers(+) and surfactant molecules (T). According to the representation inFIG. 1, the washing liquid (for example water and cleaning agent)flowing out of a pipe 1 is electrified by an electrification electrodein the form of a bare metallic electrode 2. Some of the soil 4 on theobjects to be cleaned 3 is dissolved more readily, because surfactant Tis more effectively guided to soil 4. The washing liquid can morereadily enter the interface and lift the soil 4 by penetrating under itssurface. Necessary for the appearance of the effect of electrocapillarycleaning assistance is an electric field, particularly one that has acomponent perpendicular to the surface to be cleaned. This componentcan, in the presence of surfactant T, be substantially smaller thanrequired by the theory of electrocapillarity for bringing about aneffect in the absence of a surfactant T. It is possible in this mannerto achieve cleaning assistance regardless of the kind of thecounterelectrode, not shown in FIG. 1. Such a counterelectrode (notshown in FIG. 1) can be implemented selectively in the vicinity of theobjects to be cleaned 3, but it can also be omitted, in which case themetallic objects present in the vicinity, for example the boundary ofthe internal cleaning space, can act as the counterelectrode. Becausethere is preferably no appreciable current flow, the objects acting asthe counterelectrode do not have to be electrically connected to thehigh-voltage source. The flow of washing liquid between the nozzleacting as first electrode 2 and the objects to be cleaned 3 does nothave to be continuous, because the electrified, charged washing liquidretains its charge even without contact with the electrifying electrode2. Preferably, the electrified washing liquid is electrically dischargedbefore it is removed from the inner space.

FIG. 2 shows a schematic representation of a first embodiment of theapparatus of the invention which is also suitable for carrying out themethod of the invention. Such an apparatus was used to show theimprovement in cleaning action as a result of the use ofelectrocapillary cleaning assistance on porcelain dishes soiled with amixture of oatmeal gruel and starch. To this end, the dishes 3 in theapparatus shown in FIG. 2 were sprayed with electrified or withnonelectrified washing liquid. The washing liquid emerged from pipe 1and was electrified with the aid of an electrification electrode in theform of a metallic electrode 2. The objects to be cleaned were porcelaindishes 3 to which had been applied a defined soil of oatmeal gruel andstarch 4. The solution was collected in a collecting container 6 intowhich was immersed a grounded de-electrification electrode in the formof a metallic electrode 7. At varying times, the size of the areas fromwhich soil film 4 had been removed was measured.

FIG. 3 shows two curves illustrating the removal of a test soil 4 fromthe objects to be cleaned 3 for an electrified and a nonelectrifiedwashing liquid. The apparatus shown in FIG. 2 was used for this testunder conditions explained in the foregoing. The size of the surfacearea from which the soil had been removed was measured as a function oftime.

In FIG. 3, the relative soil removal in percent is plotted along the Yaxis, with 100% corresponding to complete cleaning, while the time inminutes is plotted along the X axis. Curve K1 shows the cleaning resultsfor an electrified washing liquid, whereas curve K2 shows the cleaningresults for a nonelectrified washing liquid according to the prior art,referring to the apparatus of FIG. 2. Curve K1 refers to the case of awashing liquid electrified with 3500 volts. A comparison of curves K1and K2 shows clearly that by generating an electric field according tothe invention, much better cleaning results were obtained in a muchshorter time.

By the present invention and based on the prior art, additional savingsin operating resources (time, energy, water, cleaning agent) can beachieved, particularly for dishwashing machines. For example, spraynozzles 1 of a dishwashing machine can be provided with a high voltagewhich will result in electrification of the washing liquid 5 used. Nospecial washing liquid is needed for this purpose. The rotation ofnozzle arm 1 which is common for dishwashing machines and thus thepulsed spraying onto individual dish regions will bring about mechanicalremoval of the dislodged soil 4 without negatively affecting theelectrocapillary cleaning assistance. This effect can be furtherenhanced by the temperature of the washing liquid. The electric fieldsused according to the invention, particularly electrostatic fields, havehigh field strength, but the current flow is preferably so low that theresulting power level is harmless to humans. By limiting these electricfields, for example, to the inner washing space, and by the presence ofa current-limiting device which will shut off the power when anappreciable current arises, the user is exposed to no adverse effects.Moreover, it is possible to provide parts supplied with high voltage,for example a collecting container 6 or an internal housing, with ade-electrification electrode 7 in the form of a leak resistor.Preferably, before being removed by pumping, the washing liquid iselectrically discharged via the grounding means of the apparatus.

FIG. 4 shows a schematic representation of a second embodiment of theapparatus of the invention in the form of a dishwashing machine.According to the representation in FIG. 4, a nozzle arm 1 from which thewashing liquid is supplied by pumping is provided with anelectrification electrode 2 that is connected to a high-voltagegenerator 11 via an insulated high-voltage line 15. Positive or negativedirect current or alternating current is supplied to electrificationelectrode 2. The electrified washing liquid 5 flows over the objects tobe cleaned 3 held in an insulated rack 8. The washing liquid iscollected in a collecting container 6 whence it is recycled to nozzle 1by a pump 9 through an insulating plastic line 10 the liquid-filledparts of said pump preferably being electrically insulated. Thecollecting container is equipped with a de-electrification electrode inthe form of a grounded leak resistor 7, the purpose of this electrodebeing to ensure a safe operation. Additional technical devices 12, knownin and of themselves, of the dishwashing machine shown in FIG. 4 areinsulated either from the electrified washing liquid or from the outerhousing 13. Outer housing 13 is preferably grounded via a protectivegrounding contact and insulated from the electrified washing liquid 5.This is accomplished either in that the inner housing 14 of thedishwashing machine is made of a plastic material, or said inner housing14 is a metallic housing that is electrically completely insulated fromthe outer housing 13 and/or from the washing liquid 5. Although this isnot shown in the drawing, the electrification of washing liquid 5 can becarried out at a different point, for example by applying a high voltageto the dish rack. The washing liquid is electrified regardless of thepresence of dissolved additives. The presence of cleaning agentscontaining surface-active substances, however, was found to beparticularly advantageous for cleaning.

The foregoing description of embodiments of the present invention isprovided only for illustrative purposes and is not intended to limit theinvention. Various changes and modifications are possible within theframework of the invention without exceeding the scope of the inventionor of the equivalents thereof.

1-30. (Cancelled).
 31. A method for cleaning an object, the methodcomprising: bringing the object to be cleaned in contact with a washingliquid; and generating at least one electric field in at least a portionof a surface of the object to be cleaned.
 32. The method according toclaim 31, wherein the electric field has a perpendicular component overthe surface of the objects to be cleaned.
 33. The method according toclaim 31, wherein the electric field is generated by one of a positiveand a negative electrification of the washing liquid.
 34. The methodaccording to claim 31, wherein the washing liquid is electrified via anelectrification electrode to which is applied an electric potential. 35.The method according to claim 31, wherein the positive or negativedirect or alternating potential is in the range from 100 to 10,000 voltsand particularly from 1000 to 5,000 volts.
 36. The method according toclaim 31, wherein the washing liquid contains substances with cleaningability, particularly surfactants and/or enzymes.
 37. The methodaccording to claim 31, wherein the electrification electrode is disposedin a region of a section of a line through which the washing liquidflows before coming in contact with the objects to be cleaned.
 38. Themethod according to claim 31, wherein the electrification electrode isdisposed in the region of a nozzle arm.
 39. The method according toclaim 31, wherein a counter-electrode is disposed in the vicinity of theobjects to be cleaned.
 40. The method according to claim 31, whereinafter coming in contact with the objects to be cleaned the washingliquid is collected in a collecting container.
 41. The method accordingto claim 31, further comprising the step of at least partiallyde-electrifying the washing liquid after the step of bringing the objectcleaned in contact with a washing liquid.
 42. The method according toclaim 31, further comprising the step of at least partiallyde-electrifying the washing liquid before the step of disposing thewashing liquid.
 43. The method according to claim 31, wherein thede-electrification is carried out with the aid of a de-electrificationelectrode.
 44. The method according to claim 31, wherein thede-electrification electrode is disposed in the region of the collectingcontainer.
 45. An apparatus for carrying out the method according toclaim
 31. 46. An apparatus for cleaning objects which brings the objectsto be cleaned in contact with a washing liquid, wherein the apparatusincludes means capable of generating at least one electric field in atleast some regions of the surfaces of the objects to be cleaned.
 47. Theapparatus according to claim 46, wherein the means generate the electricfield so that said field has a perpendicular component over the surfaceof the objects to be cleaned.
 48. The apparatus according to claim 46,wherein the means electrify the washing liquid.
 49. The apparatusaccording to claim 16, wherein the washing liquid contains substanceswith cleaning ability, particularly surfactants and/or enzymes.
 50. Theapparatus according to claim 16, wherein the means for electrifying thewashing liquid comprise an electrification electrode to which anelectric potential can be applied.
 51. The apparatus according to claim16, wherein the positive or negative, direct or alternating potential isin the range from 100 to 10,000 volts and particularly from 1000 to5,000 volts.
 52. The apparatus according to claim 16, wherein theelectrification electrode is disposed in the region of a section of theline through which the washing liquid flows before coming in contactwith the objects to be cleaned.
 53. The apparatus according to claim 16,wherein the electrification electrode is disposed in the region of anozzle arm.
 54. The apparatus according to claim 16, further comprisinga counterelectrode disposed in the vicinity of the objects to becleaned.
 55. The apparatus according to claim 16, wherein metallicobjects of the apparatus or metallic objects to be cleaned take over thefunction of the counterelectrode.
 56. The apparatus according to claim16, wherein, after having been brought in contact with the objects to becleaned, the washing liquid is collected in a collecting container. 57.The apparatus according to claim 16, further comprisingde-electrification means for the purpose of at least partiallyde-electrifying the washing liquid after said washing liquid has atleast once been brought in contact with the objects to be cleaned. 58.The apparatus according to claim 16, wherein the de-electrificationmeans de-electrify the washing liquid at least partially before saidwashing liquid is disposed of.
 59. The apparatus according to claim 16,wherein the de-electrification electrode is located in the region of thecollecting container.
 60. The apparatus according to claim 16, furthercomprising a protective circuit breaker which shuts off the electricpower when a pre-determined current flow is exceeded.
 61. The apparatusaccording to claim 16, wherein the apparatus is a dishwasher.